1. Field of the Invention
The present invention relates to automated assembly machines and, more particularly, to an automated assembly machine having clamp assemblies which are automatically adjustable so that the machine may be used to build assemblies of various sizes and shapes.
2. Background Art
In recent years major advances have been made in the use of machines for automatically fastening both large and small assemblies of parts together to produce various subassemblies, many of which are very large. In particular, such automated assembly tools have proven especially effective in the assembly of major aircraft subassemblies, such as wing spars for commercial transports.
For a long period beginning during World War II, such major subassemblies were produced by hand, which required the expenditure of vast numbers of man-hours for each aircraft. Relatively recently, however, significant improvements in efficiency have been achieved through the use of automated assembly tools, such as those disclosed in U.S. Pat. Nos. 4,203,204 and 4,310,964, both of which share the same assignee as the present application, and both of which are hereby incorporated by reference in their entireties. Although it is beyond the scope of the present application to describe these automated assembly tools and their associated computer controls in detail, it will be useful at this point to consider an overview of these devices, as they relate to the present invention.
FIG. 1 shows an automated assembly machine 10 such as that which is disclosed in the above-referenced patents. Machine 10 includes a framework 11, which comprises a plurality of C-shaped frames 13, each of which includes a vertical beam 15 and upper and lower horizontal beams 17 and 19. Mounted on upper and lower horizontal beams 17 and 19, so as to span the frames 13, are pedestal beams 25 and 31. Also mounted on lower beams 19 is a platform 27, the edges of which are spaced apart from lower pedestal beam 25 so as to form a channel 28. A series of vertically aligned pairs of pedestals 39 are mounted on pedestal beams 31 and 25, and mounted at the ends of the pedestals 39 are part locating and holding devices 41, which support the subassembly in a vertical plane. The specific subassembly illustrated in FIG. 1 is a spar 43, which comprises a vertically oriented web 45, lower and upper chords 47 and 48, and a plurality of transversely positioned stiffeners 49.
As shown in FIG. 2, the part holding devices 41 include a housing which comprises a pair of vertically extending sidewalls 42, a base 44, and a backwall 46. The base 44 is bolted to the related pedestal 39. Flanges 50 extend from sidewalls 42 at the front of the housing, and support a rotatably mounted shaft 54, to which is affixed a pinion gear 56. Pinion gear 56 is engaged by rack 66, the end of which is attached to the shaft 68 of a pneumatic actuator 70. When the pneumatic actuator 70 is energized, its shaft 68 moves rack 66 back and forth, causing gear 56 and shaft 54 to rotate, in turn causing a C-shaped clamp arm 58 which is mounted to the end of shaft 54 to rotate between the phantom and solid line positions illustrated in FIG. 2; in the solid line position, the components to be assembled are gripped in the part locating and holding device 41.
Assembly of the spar subassembly components is accomplished by movable carriage-mounted tools under the direction of a computerized control assembly. (See FIG. 1.) Guide rails 55 and 61 are mounted adjacent to the lower and upper pedestal beams to guide and support the main carriage assemblies, each of which includes a horizontal carriage 67 and a vertical carriage 69. The vertical carriages support various tools for clamping and drilling holes in the spar assembly 43, and for installing fasteners therein. The horizontal carriages 67 include vertically oriented threaded shafts 72, which are rotated by motors 74 and which pass through nuts 78 mounted on vertical carriage 69; when threaded shafts 72 are rotated, the vertical carriages move vertically relative to the horizontal carriages. Encoders 76 are mounted to the ends of the shafts 72 for registering their rotation. Horizontal carriages 67 are also provided with drive mechanisms (not shown) which propel them horizontally along rails 55 and 57. As carriages 67 move back and forth, power is supplied to them through flexible power tracks 80. An example of a suitable power track is the Aero-Trak.TM. produced by Aero-Motive Manufacturing Company of Kalamazoo, Michigan. This necessitates the channels 28 between pedestal beam 25 and platforms 27 and 82, which accommodate the passage of the power and signal wire bundles from the power track movable end to the carriages 67.
Associated with automated assembly tool 10 is a computerized control assembly 84, which includes a controller 86, a magnetics ("MAG") cab 87 which contains various relays, and an electromagnetic riveting ("EMR") cab 88 which contains the power supply for installing the fasteners. Once the components of wing spar assembly 43 have been positioned in and engaged by part holding devices 41, control assembly 84 directs the movements of the horizontal and vertical carriages relative thereto, and the drilling of holes and installation of fasteners therein.
While the prior art automated assembly tools such as that just described have represented a tremendous advance over earlier assembly methods, they have been afflicted with a number of drawbacks which limit their adaptability and efficiency. Perhaps most serious of these deficiencies is the fact that each automated assembly tool is dedicated to producing a single subassembly. In other words, the particular automated assembly tool is capable of producing only a single type or design of subassembly (e.g., particular design of wing spar), and cannot be used to assemble subassemblies having other designs, sizes, shapes, or contours. This is a serious drawback in the manufacture of commercial aircraft, being that such aircraft may include a great many wing spars, ribs, bulkheads, and panel assemblies having various contours. This limitation is due in large part to the fact that the supporting pedestals 39 for the part holding devices 41 are nonadjustable in length. As the distance between the vertical aligned pairs of holding devices is thus fixed, these can only accommodate a component having that particular height at that position. It may thus be seen in FIG. 1 that the support columns 39 of prior art machine 10 have various fixed lengths, the lengths being selected so that the fixed locations of the associated holding devices 41 correspond to the curved contours of the upper and lower cords 48 and 47 of the wing spar subassembly 43. A further drawback is that these holding devices 41 themselves are not adaptable to accommodate parts having various shapes.
Another deficiency of the prior art automated assembly tools has involved the channels 28 which are required to accommodate the passage of the signal and power supply wires through the support platforms. These channels represent a potential safety hazard for personnel manning the assembly tool, who must step over the channel to gain direct access to the subassembly or the carriages, and in some cases this has necessitated the construction of special bridges over the channels.
Accordingly, there exists a need for an automated assembly tool which is capable of accommodating and holding components of various sizes, shapes, and contours, so that these can be assembled. Furthermore, there exists a need for an automated assembly tool which avoids the use of channels in the supporting platforms about the components being assembled.